Both of these are good suggestions.

A friend of mine was coming back from Amsterdam last summer and had a Bic Pen that had been used in making a pipe. It had some resin inside the shaft and he got a paraphenalia ticket.

Mailing it ahead is probably your best bet. If you can't do that definately pack it inside your checked luggage, inside of something that will cover it when it goes through the X-ray. [I hear a box lined with aluminum foil works wonders.] Most of the time they won't check it because it won't look like a bomb or drugs. And if it hasn't been used there's no way to really detect if, even if they have dogs around.

I wish you the best of luck in both shopping and transporting it back.